The inventive concept relates to image processing devices, and more particularly, to methods of automatically adjusting white balance in image processing devices.
White balancing is a process of determining that a pixel or a collection of pixels (hereafter, a “patch”) selected from an input image is white in color and thereafter adjusting color(s) of the image, wholly or in part, according to one or more gain(s) of a color difference component (i.e., R or B) of the determined pixel or patch. A white patch having a color variance for an imaged object due to an illuminance condition for the image data is applied to adjust a white balance that may vary with a color temperature is determined using a red, green, blue (RGB) ratio of the detected patch (or pixel). Color correction for shifting a total color sense and tuning a color balance is performed by adjusting a gain of a red (R) and a blue (B) of an image according to the color temperature.
Generally, when the same object is imaged (e.g., in a still image) using various kinds of imaging devices such as a digital camera, the color appearance of the image changes in accordance with different illuminance conditions (e.g., a white lighting, fluorescent lighting, sun light, etc.). The human eye possesses a color constancy, such that a human recognizes white color under different luminance conditions. However, an image device may recognize the color of an object based on a RGB component included in different illuminance conditions. For example, when a color temperature of a particular illuminance condition is high, the image device may reproduce “white” including a blue color component of the image. On the other hand, when a color temperature of another luminance condition is low, the image device may reproduce “white” including a red color component of the image.
Accordingly, when a color temperature changes due to an illuminance condition, there is a need to adjust a white balance that correctly renders a white color. For example, a white color including a blue color is adjusted so as to increase a gain of a red (i.e., R) and decrease a gain of a blue (i.e., B). On the other hand, a white color including a blue color is adjusted so as to increase a gain of a red (i.e., R) and decrease a gain of a blue (i.e., B). A white component which is a reference of a white balance is accurately detected to accurately adjust the white balance. However, an auto white balance (AWB) having a complexity and a high cost may be used to accurately detect a white component. Accordingly, there is a need to implement a high-speed and low-power auto white balancing approach such that incorporating devices are suitable for mobile use.